The Phases of Clinical Trials

In Phase 1 the investigators of a new drug or vaccine spend months looking at the effects on a group of 20-100 people who have no underlying health conditions. This is to figure out what sort of dose is required and how they react to it. This is because new drugs or vaccines can be unpredictable depending on how the drug is administered. If it reaches about 70% it then passes onto phase 2.

So, it’s really about theoretical effectiveness.

In phase 2 of an investigation the numbers are increased to the hundreds, so 200-500 people that are given the safest dose for the desired effects. These are then monitored between months and years to see if it is continuing to be safe and to gather information on longer term side effects.

This information is then used to go onto and monitor stage three. About 35% pass this stage.

So, it’s really about safety.

Stage 3 is the most important, about working with random trials so claims are not purely subjective based on effectiveness and safety. Essentially the drug or vaccine working because information is being biased in favour of it working. This means using 3,000-10,000 randomly selected individuals who have the disease the drug or vaccine is supposed to work on. The trials need to be what is called double blind so that the people receiving the treatment don’t know if they have had the specific treatment, and those testing don’t know if the recipient has had the specific treatment. This can last for years while information is collected as how a disease develops is very important. The treatment needs to be proven to be as safe and as effective as alternative treatments or not being treated at all. This is when long term or rare effects are found. About 20% pass this level.

So it’s really about proving claimed results.

If a drug or vaccine passes all three levels then as long as the data says it’s effective and safe it can go into manufacture and use, but still needs widespread monitoring as the numbers it is used by increase dramatically. This is when long term safety is defined.

Numbers involved at each stage                     Time

Stage 1                        20-100                         1-6 months

Stage 2                        200-500                       3-6 months

Stage 3                        3,000-10,000               6 months – 3 years

Use                              1 million +                  10 years

The minimum time is probably 10 months for a limited use drug or vaccine with minimal permitted checking at each stage. Some of these can overlap, but quite often the results from one are needed to set the base level for the subsequent one, without it the results getting a grey area picture rather than being distinct.